The present invention relates to an O/W type aqueous thermosetting resin dispersion which comprises mixing a liquid radical polymerization type thermosetting resin and water together to disperse particles of the resin in the aqueous phase. Moreover, the present invention also relates to an FRP precision filter medium comprising a porous cured material that is obtained by curing the above-mentioned O/W type aqueous thermosetting resin dispersion in the presence of a reinforcing material and which has approximately spherical fine particles bound together therein and communicating voids between the bound particles, and a manufacturing method thereof.
Regarding aqueous dispersions obtained by mixing a radical polymerization type thermosetting resin such as an unsaturated polyester resin or an epoxy acrylate resin and water together and carrying out dispersion, conventionally ones in which water droplets are dispersed in the resin, i.e. W/O emulsion type aqueous thermosetting resin dispersions, are known, and indeed are commercially sold. Such conventional W/O emulsion type aqueous thermosetting resin dispersions are used as one method of incorporating moisture into a resin to make the resin fire-resistant, and are also used as means of suppressing cure shrinkage of unsaturated polyester resins and epoxy acrylate resins.
Moreover, regarding aqueous dispersions obtained by mixing a radical polymerization type thermosetting resin such as an unsaturated polyester resin and water together and thus dispersing particles of the resin in the aqueous phase, due to the belief that the binding between the resin particles will be poor and hence it will not be possible to obtain a cured material having a mechanical strength sufficient to withstand practical use, up until now there have been virtually no studies carried out on O/W type aqueous dispersions obtained by mixing a radical polymerization type thermosetting resin such as an unsaturated polyester resin and water together and carrying out dispersion.
The present inventors carried out a multitude of studies on radical polymerization type thermosetting resins such as unsaturated polyester resins, epoxy acrylate resins and urethane acrylate resins, and as a result discovered O/W type aqueous dispersions obtained by mixing a radical polymerization type thermosetting resin and water together to uniformly disperse particles of the resin in the aqueous phase. It was also discovered that such an aqueous dispersion is stable and thixotropic and has excellent workability, and moreover that the aqueous dispersion can be cured at ambient temperature or with heating as with a conventional radical polymerization type thermosetting resin, and the cured material obtained has fine interconnected pores and is able to withstand practical use.
That is, the O/W type aqueous thermosetting resin dispersion of the present invention can easily be cured at ambient temperature or with heating by adding a curing agent and if necessary an accelerator, and a porous cured material having fine interconnected pores can be obtained; this porous cured material, if treated to increase the functionality, can be used in various applications, for example as a precision filter medium, or as an absorbent/adsorbent, or as a carrier.
Conventionally, organic films, hollow fibers, ceramics, metal films and so on are known and are commercially sold as precision filter medium for sewage treatment. However, organic films must be assembled in a cell for filtration, and hence there are drawbacks such as there being a cost to manufacture the cell and the durability of the cell being poor. Hollow fibers have the advantage of being small and light, but are expensive. Ceramics are inexpensive as materials, but have the drawbacks of being heavy and the size becoming large. Metal films can be freely shaped and have durability in terms of strength, but have the drawbacks of being expensive and of the durability worsening through corrosion, and hence the current state of affairs is that they are not widespread on the market.
Consequently, based on the realization that up until now it has not been possible to obtain a cured material able to withstand practical use, it is an object of the present invention to provide a stable O/W type aqueous thermosetting resin dispersion comprising an aqueous dispersion obtained by mixing a radical polymerization type thermosetting resin and water together to uniformly disperse particles of the resin in the aqueous phase, this being a type of aqueous dispersion that has hardly been studied hitherto.
Moreover, it is an object of the present invention to provide a precision filter medium, which comprises a porous cured material obtained by curing the O/W type aqueous thermosetting resin dispersion in the presence of a reinforcing material, is light and durable, can be freely shaped, and is satisfactory in terms of cost, as well as a method of manufacturing the precision filter medium.
The present invention relates to an O/W type aqueous dispersion which comprises mixing a radical polymerization type thermosetting resin, for example a radical polymerization type thermosetting resin such as an unsaturated polyester resin, an epoxy acrylate resin or a urethane acrylate resin, and water together and carrying out dispersion so that particles of the resin are uniformly dispersed in the aqueous phase; the aqueous dispersion is stable and thixotropic and has excellent workability; moreover, as with a normal radical polymerization type thermosetting resin, the aqueous dispersion can be cured at ambient temperature or with heating by adding a curing agent and if necessary an accelerator, and the cured material obtained is a porous cured material having fine interconnected pores that can withstand practical use.
Moreover, the cured material is light, and the majority of the fine interconnected pores in the cured material have a pore diameter in a range of 0.1 to 1.0 xcexcm, with there being hardly any pores that colon bacilli of size 1 xcexcm or more will pass through, and hence it was found that the cured material is suitable for precision filtration. It was ascertained that a cured material obtained by curing the aqueous dispersion in the presence of a reinforcing material has sufficient strength, and can be used as a precision filter medium having excellent durability; moreover, because an aqueous dispersion of a radical polymerization type thermosetting resin is used, there is freedom in the molding, and hence molded articles of various shapes can easily be obtained, and thus problems of conventional precision filter media can be resolved all at once.
Specifically, the present invention relates to: (1) an O/W type aqueous thermosetting resin dispersion which comprises mixing a liquid radical polymerization type thermosetting resin and water together in a weight ratio in a range of 90:10 to 60:40 to uniformly disperse particles of the resin in the aqueous phase; (2) the O/W type aqueous thermosetting resin dispersion of (1) above, wherein the liquid radical polymerization type thermosetting resin comprises at least one selected from liquid unsaturated polyester resins, liquid epoxy (meth)acrylate resins, liquid urethane (meth)acrylate resins and liquid (meth)acrylic resins; (3) as above, wherein the liquid radical polymerization type thermosetting resin is a liquid radical polymerization type thermosetting resin containing a curing agent; and (4) as above, wherein the liquid radical polymerization type thermosetting resin is a liquid radical polymerization type thermosetting resin containing a curing agent and an accelerator.
Moreover, the present invention relates to: (5) an FRP precision filter medium, characterized by comprising a porous cured material, which is obtained by curing an O/W type aqueous dispersion comprising a liquid radical polymerization type thermosetting resin in the presence of a reinforcing material, has approximately spherical fine particles bound together therein and communicating voids between the bound particles, and has fine interconnected pores having an effective pore diameter of 0.1 xcexcm to 1.0 xcexcm and a porosity of 10 to 40 vol %.
Furthermore, the present invention relates to: (6) a method of manufacturing an FRP precision filter medium, characterized by comprising a porous cured material having fine interconnected pores having an effective pore diameter of 0.1 xcexcm to 1.0 xcexcm and a porosity of 10 to 40 vol %, which is obtained by curing, at ambient temperature or with heating, in the presence of a reinforcing material, an O/W type aqueous thermosetting resin dispersion that has been obtained by mixing a liquid radical polymerization type thermosetting resin and water together in a weight ratio in a range of 90:10 to 60:40 to uniformly disperse particles of the resin in the aqueous phase, and then removing water and drying at ambient temperature or with heating.